They are only defectable if the cop that pulls you over has nothing else to defect you for.
They are not in your line of sight or will cause you to bang your head on it in an accident as the seat belt tention will kick in before you get close to head butting it, and if you have an airbag the airbag will also kick in.
If they are defectable then every taxi in Australia is defectable as they all have that LCD display communication thing in the same spot, and if you look in a cop car they have a whole heap of shit in that same location!!